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Re: [Qemu-devel] [PATCH v12 09/10] qcow2: skip writing zero buffers to e

From: Alberto Garcia
Subject: Re: [Qemu-devel] [PATCH v12 09/10] qcow2: skip writing zero buffers to empty COW areas
Date: Tue, 15 Jan 2019 16:27:59 +0100
User-agent: Notmuch/0.18.2 (http://notmuchmail.org) Emacs/24.4.1 (i586-pc-linux-gnu)

On Mon 14 Jan 2019 12:18:30 PM CET, Anton Nefedov wrote:
> If COW areas of the newly allocated clusters are zeroes on the backing image,
> efficient bdrv_write_zeroes(flags=BDRV_REQ_ALLOCATE) can be used on the whole
> cluster instead of writing explicit zero buffers later in perform_cow().
> iotest 060:
> write to the discarded cluster does not trigger COW anymore.
> Use a backing image instead.
> Signed-off-by: Anton Nefedov <address@hidden>
> Reviewed-by: Vladimir Sementsov-Ogievskiy <address@hidden>

Reviewed-by: Alberto Garcia <address@hidden>

> +        ret = handle_alloc_space(bs, l2meta);

I insist that it would be nice to have a short comment explaining what
this does.


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